Atherosclerotic vascular disease is a major cause of morbidity and mortality in the United States. The pleiotropic process in human atherogenesis remains unknown. Lipid accumulation in smooth muscle cells (SMC) and macrophages represent a characteristic feature of atherosclerotic plaque. The aberrant lipid uptake is possible related to activity of low density lipoprotein (LDL) receptor and scavenger receptor as well as to cholesterol metabolism. At the sites of atherosclerotic lesions, endothelial cells (EC) are known to be activated. Potential mediators released from activated EC may in turn affect the cholesterol metabolism of SMC and macrophages via LDL receptor and scavenger receptor. My preliminary data suggested a link between the effect of endothelial cell-derived mitogens on the regulation of LDL receptor and cholesterol metabolism in SMC. Specifically, the LDL regulated by mitogens including bFGF is at three levels: (i) enhance the synthesis of receptor surface protein, (ii) induce the receptor mRNA, (iii) up-regulate the transcription of receptor gene. In addition, bFGF regulated cholosteryl metabolic enzymes activity and increased cholesterol esterification have been found. The overall objective of this grant proposal is to define the role of endothelial cell-derived mitogens in the regulation of cholesterol metabolism in arterial smooth muscle cells and macrophage in the context of atherosclerosis. The experiments proposed in Specific Aim 1: Using kinase inhibitors and PKA- and PKC- deficient cells, I will examine signal transduction pathways mediated by EC-derived mitogen and correlate the alteration to the regulation of LDL receptor on SMC. In addition, I will study the transcriptional regulation of the LDL receptor by mitogens and to dissect the regulatory role of transcription factors. In Specific Aim 2. I will study and examine the effects of EC-derived mitogen on SMC cholesterol metabolism; and, specifically to characterize the mechanisms of cellular mediators in regulating the interaction between LDL receptor and cholesteryl ester metabolic enzymes. A causal relationship between the mitogen-induced receptor kinase and second messengers and the regulation of the function of LDL receptor gene and cholesterol metabolism will be established. Moreover, to extend these studies to what occurs in vivo, I will evaluate using an in vitro coculture system detailed in Specific Aim 3. I propose to study the transcellular modulation of cholesterol metabolism in the two-cell coculture system between EC and macrophages. Specifically, I will evaluate the role of cell to cell interactions in the regulation of LDL receptor/scavenger receptor and cholesterol trafficking on macrophages. These studies in my proposal should aid in the understanding of the mechanisms of progressing and regressing foam cells development in the atherosclerotic process, and thus lead to the discovery and development of drugs to thwart the progression of atherosclerotic disease.